1. Field of the Invention
This invention relates to the field of an optical switch element and a wavelength router.
2. Description of Related Art
Conventionally, optical switches comprise a plurality of switch elements arranged in a matrix, have functions for emission from prescribed output ports of signals which have been input from a plurality of input ports, and are used as modules indispensable for the realization of optical communication systems.
Reference I (xe2x80x9cSelf-Latching Waveguide Optical Switch Based on Thermo-Capillarityxe2x80x9d, ECOC97, 22-25 1997, Conference Publication No. 448, IEE, 1997, pp. 73-76) discloses one example of such a switch element. In Reference I, an element is disclosed in which a movable reflecting mirror provided at the intersection of mutually orthogonal bus line waveguides is used, by which means signal light is made to either propagate rectilinearly or to be reflected, so that input light is caused to be output from different output ports.
By means of such an optical switch element, signal light caused to be input from one input port can be made to be output from a selected output port. Hence a plurality of these optical switch elements can be combined to realize a multiple-stage input/output optical switch.
However, the optical switch of Reference I has the following defect. In the optical switch of Reference I, each switch element has a movable reflecting mirror in order to change the optical path of input light, and so losses arising from this occur in each switch element. As a result, the total loss in an optical switch comprising numerous switch elements is extremely large. Specifically, a loss as large as approximately 2 dB occurs at the one mirror of each switch element. One reason for this is the fact that each switch element is extremely small.
That is, reflected light is given as a superpositioning of a plurality of light rays backscattered due to the existence of the scattering object. Consequently, when the object itself becomes approximately as small as the light wavelength, it becomes difficult to obtain adequate reflected light.
Hence in the optical switch element of Reference I, losses in the mirrors provided in optical paths is great, and so when configuring an integrated multiple-stage input/output optical switch, these losses are cumulative, and an extremely large loss occurs. If the losses of each switch element cannot be reduced, it is not possible to realize a low-loss large-scale optical switch adequate for practical use.
An object of this invention is to provide an optical switch element in which the excess losses at individual optical switch elements can be reduced, so that a low-loss large-scale optical switch adequate for practical use can be configured.
To this end, the optical switch element of this invention is configured as follows. The optical switch element of this invention comprises a substrate; a plurality of optical waveguides (equivalent to a core) on the substrate, surrounded by cladding and mutually intersecting; an optical wave-guiding member, provided in the vicinity of these intersecting parts and capable of optical coupling of each of the optical waveguides; and control means to apply state changes to the optical wave-guiding member in order to control the refractive index. The optical wave-guiding member, each of the optical waveguides, and the cladding are formed such that the refractive index of the optical wave-guiding member is effectively the same as, or higher than, the refractive index of the optical waveguides when in the first state, and is effectively the same as the refractive index of the cladding when in the second state.
In this configuration, when the optical wave-guiding member is in the second state, signal light input to a port equivalent to an end of one optical waveguide of this optical switch element is output from a port equivalent to the other end of the optical waveguide. On the other hand, when the optical wave-guiding member is in the first state, signal light input to an end of one waveguide is transferred to the optical wave-guiding member, which has a refractive index that is effectively the same as or higher than that of the optical waveguide, and then is transferred from the optical wave-guiding member to another optical waveguide. Hence by using control means to control whether the optical wave-guiding member is in the first or the second state, the optical path of signal light input to the optical switch element can be changed, and so operation as an optical switch element can be realized.
This invention also provides a wavelength router by operating the above-mentioned wave-guide member as a ring-type resonator.
The wavelength router of this invention comprises a substrate; a plurality of optical waveguides (equivalent to a core) on the substrate, surrounded by cladding and mutually intersecting; a ring-type resonator, provided in the vicinity of these intersecting parts and capable of optical coupling of each of the optical waveguides; and control means to apply state changes to the optical wave-guiding member in order to control the refractive index. The ring-type resonator, and the cladding are formed such that the refractive index of the optical ring-type resonator is effectively higher than the refractive index of the cladding when in the first state, and is effectively the same as the refractive index of the cladding when in the second state.
In this configuration, suppose that the ring-type resonator is in the first state. In this state, suppose that light is input to a port equivalent to the end of one optical waveguide of the wavelength router. Of this input wavelength-multiplexed light, light at a specific wavelength coinciding with the resonance wavelength of the ring-type resonator, after transfer to the ring-type resonator, is transferred to another optical waveguide, and is output from a port equivalent to an end of the other optical waveguide. The wavelength-multiplexed light with other than the specific wavelength is output from a port equivalent to the other end of the single optical waveguide. On the other hand, suppose the ring-type resonator is in the second state. In this case, wavelength-multiplexed light input to a port equivalent to one end of an optical waveguide is output from the port equivalent to the other end of the optical waveguide. That is, this wavelength router functions as a wavelength router capable of switching between demultiplexing and non-demultiplexing.